A branchline coupler is a quadrature coupler, consisting of circuitry in an entirely single plane of a semiconductor device. For example, the branchline coupler consists of four strip line ports coupled to each other by two transversal lines or bridges, all of which lay in a same plane. In an ideal branchline coupler, each transmission line is a quarter wavelength; although, other wavelengths are also possible such as 3/4, 5/4 or 7/4 wavelengths (etc.). In operation, for example, a signal entering a Vin port is split into two quadrature signals, with the remaining port fully isolated from the input port at the center frequency.
In a branchline coupler, bond wires for the common ground add inductances and make the branchline coupler more susceptible to ground bounce and performance degradation. Also, as the branchline coupler consists of circuitry in an entirely single plane, valuable chip real estate is realized in the fabrication of the branchline coupler.